This invention relates to improved methods and apparatus to detect patients with an abnormally altered perception of dyspnea. Of particular concern are asthma patients at risk for fatal asthmatic attacks. An unexpected rising incidence of fatal asthmatic attacks in recent years has been of concern to the medical profession.
The sensitivity of the testing procedure is enhanced by the test being performed under controlled conditions by having the patient breathe in a precisely defined manner by visual biofeedback means, with the subject following a predetermined breathing pattern on a computer CRT or similar means. Hillsman incorporates by reference his U.S. Pat. No. 3,991,304 which describes a sophisticated method to prompt patients to desired breathing patterns by visual biofeedback means.
Prior art has indicated patients who have survived a near fatal asthma attack have decreased dyspnea awareness to increased inspiratory resistance (See: LOWERED CHEMOSENSITIVITY AND PERCEPTION OF DYSPNEA IN PATIENTS WITH NEAR--FATAL ASTHMA-- Kikuchi, Y. et all, Respiratory and Critical Care Medicine, Supplement, Volume 149, Number 4, April 1994). The cited investigators demonstrated decreased dyspnea awareness in near fatal asthma patients by imposing graded inspiratory respiratory resistance from zero to minus 30 cm. water/liter/second gauge pressure. But no attempt was made by these investigators to further control the experimental conditions by defining the testing tidal volume to the patient's available lung volume as reflected in the patient's vital capacity, or the testing inspiratory resistance load to the patient's available maximum inspiratory pressure capability. Further, no attempt was made to otherwise precisely control the patient's breathing pattern or the precise timing of the breathing stages under the testing conditions, or to otherwise detect whether or not the subjects were performing as required under the testing conditions. Therefore, absent comprehensive controlled breathing conditions the testing achieved was relatively crude and therefore less sensitive to defining and detecting dyspnea awareness as measured by the commonly used Borg scale of dyspnea, and likewise there was no assurance as to patient performance and therefore data reliability.
In addition, there are many patients with Hyperventilation Syndrome, who perceive they have dyspnea when in fact their respiratory function is normal, and definition and quantifying this abnormality and normalization with treatment is of value in the patient therapeutic program.
Further, many patients with dyspnea related to Chronic Obstructive Pulmonary Disease (Emphysema and Chronic Bronchitis) and other respiratory conditions undergo comprehensive Pulmonary Rehabilitation, including various measures to improve dyspnea distress. These measures include various medications, breathing exercises and breathing retraining in proper breathing patterns, respiratory muscle reconditioning and strengthening by various means, and general body reconditioning and strengthening. Present methodology to quantify dyspnea and measure improvement with the various treatment modalities has generally been controversial and unsatisfactory. Therefore, there is a need to properly define and quantify the dyspnea abnormality and any normalization with the various treatments in the patient therapeutic program, both to guide therapy and to document improvement for administrative needs.
The instant invention to comprehensively define the testing conditions relative to the patient's vital capacity and/or maximum inspiratory pressure capability, and to further define the testing conditions by having the patient breathe in a precisely controlled manner using predefined breathing patterns by visual biofeedback means, and to precisely control the sequence and timing of the testing events. Therefore, by establishing the breathing testing conditions the sensitivity, accuracy and reproducibility of the diagnostic methodology will be enhanced. In addition, by placing definable plus and minus error limits above and below the desired breathing analogs, with suitable audio and/or visual alarms to indicate if the patient breathing performance is outside acceptable limits, the diagnostician may determine whether or not the subject is performing in an acceptable manner to the testing methodology as defined by the operator for the particular subject and thereby generating reliable testing data.